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Tension tamer. In a hypothetical solid T. rex skull (top), tension accumulates beneath the eye socket when the animal takes a bite, but the tension dissipates when flexible joints are incorporated into the model (bottom).

T. rex's Shock-Absorbing Skull

The mystery of why some of the bones in the skull of Tyrannosaurus rex are loosely articulated has been solved. The unusual flexibility of the T. rex skull appears to be an adaptation for absorbing the tension generated by its aggressive biting, according to research published 9 June in the Proceedings of the Royal Society of London, Series B.

Several lines of evidence suggest that T. rex fed using a "puncture–pull" strategy, startling its prey with an extremely powerful bite and then dragging its teeth back through flesh and bone. But strangely for an animal with a tougher bite than a great white shark, some of the bones that make up a T. rex skull are not fused and would only have been held together by connective tissue. This apparent design flaw has always demanded an explanation. How could T. rex have wrought such havoc with a wobbly skull?

Now Emily Rayfield, a paleontologist at the University of Cambridge, U.K., thinks she has the answer. Finite element analysis--a computerized modeling technique often used by engineers to test for weaknesses in design--has revealed where the stresses and strains accumulate in a T. rex skull during its devastating puncture–pull feeding action. Whilst mobile joints in the cheek of T. rex do weaken the overall structure of its skull, they nevertheless serve a crucial function, the analysis reveals. "They seem to be acting as shock absorbers" to protect the surrounding bones from damage, Rayfield says.

This solves the puzzle of how T. rex could be so aggressive with this kind of flexible skull, says Gregory Erickson, a paleontologist at Florida State University in Tallahassee who first proposed that T. rex used the puncture–pull approach. "It helps explain how they got away with that behavior and what those joints were doing," he says. The model also reveals that the bone-crushing bite sends strong compressive and shear forces to the top of the skull, which might explain why Tyrannosaurids have such enlarged nasal bones and why they are fused together from an early age. "This is the start of a much more comprehensive study to really get at the nitty-gritty of the form and function of these animals," says Erickson. "I think all her conclusions are spot on."